To extract the usage of the link targets, we performed a manual labeling to all link targets from our sample (similar to [1]}).
At this stage, the authors of this paper specified the code for categorizing the usage of the links.
The initial codes used to categorize the links were imported from the study by [1]}.
However, we dropped several labels because they are unrelated to our research.
We also combined and adjusted some codes to make them appropriate to our study.
Similar to other works in classifying the link targets [1]}, four authors of this paper (the first, third, fifth, and the sixth authors) then coded the first 30 links from the representative sample independently using the designed codes.
The kappa agreement from the four raters is 0.81 or `almost perfect' [4]}.
Based on this encouraged agreement, the remaining link targets were then coded by the first author.
